A two mass feeder includes a base supported on a floor by mounting springs, a horizontal trough supported on the base by inclined leaf springs, and an electromagnetic vibrator or driver mounted between the base and trough to vibrate the trough. In this two mass (base and trough) vibratory system, a large reaction force acts on the base, which should accordingly have a large mass; but nevertheless, vibrations are transmitted to the floor through the mounting springs.
Taylor U.S. Pat. No. 3,786,912 shows a three mass feeder, which includes springs supporting an action mass having a trough and a reaction mass on a base mass. An electromagnetic driver is interposed between the action and reaction masses. The action and reaction masses have coincident centers of gravity, and more preferably, the effective lengths of the springs of the action and reaction masses are the same, in order to vibrate these masses in reverse Phase. This offsets or substantially reduces the vibration of the base mass, so that the base may be fixed to the floor. In this feeder, however, only a single track on the action mass is used to transfer articles.
Brown U.S. Pat. No. 4,378,064 shows another three mass electromagnetic feeder, which includes an electromagnet mounted, as one of the three masses, to a base by springs, and an armature fixed to the base. Horizontal vibratory force acts between the electromagnet and armature. A trough and the base vibrate in reverse phase, and the electromagnet and base vibrate in phase. This can reduce the gap between the electromagnet and armature, resulting in less electric power consumption. However, the vibration of the base is large, and only one trough is used to transfer articles.
Thus, in these prior art feeders, the vibration of only one trough or track as one of the three masses is effectively used to transfer articles, resulting in a low transfer capacity.